In conventional logging operations, the initial transportation of a felled tree from the location where it is cut to a location where it can be efficiently transported to a mill is a major logistical problem. Heretofore, temporary roads were constructed throughout the forest area being harvested thereby making the felled trees readily accessible to tractors. Generally, tractors are employed to move each felled tree to a location where it could be transferred to a more convenient mode of transportation. In recent years, however, road building costs and issues of soil compaction have significantly affected the ability to access logs by tractor. This has been particularly true in connection with logging operations carried on federally owned areas. Today there typically is a greater distance between roads, and logs often are hooked to cables or other similar lines and are dragged or skidded by a skidding machine located on one of the roads. Whereas in the past, this technique for skidding logs was used only on very steep terrain that was inaccessible to tractors, it is now being used increasingly on gentle slopes between widely spaced roads.
Log skidding carriages are used in most log skidding operations. The typical log skidding carriage employs a skyline and a drag line which extend through the carriage to a log skidding machine. The log skidding machine is located at a higher elevation than the logs to be skidded, and it can selectively pull in or let out either or both of the lines. The end of the skyline away from the skidding machine is attached to an immovable object or anchor, such as a tree. The end of the drag line away from the skidding machine is attached to the log that is to be skidded.
The typical carriage made according to prior art teachings includes a skyline sheave which rotates along the skyline. Both the skyline and the drag line generally include actuators such as metallic balls or knots near their free ends to control the movement of the carriage along the skyline as explained below.
A log skidding operation commences with the carriage close to the skidding machine. The skyline is unwound by the skidding machine, and is pulled by workers to the immovable object that functions as an anchor. The object may be a tree or tree stump. The skyline is then pulled tight between the skidding machine and the anchor. The drag line then is let out allowing the skyline sheave to roll downhill along the skyline, carrying the carriage and drag line toward the anchor point. The carriage stops moving downhill when it contacts the skyline actuator, after which the skidding machine then unwinds the drag line further and the free end of the drag line is attached to the log to be skidded. The drag line is then pulled in by the skidding machine. Once the actuator on the end of the drag line reaches the carriage, the carriage will be pulled along with the log toward the skidding machine.
This operation will be repeated many times without relocating the skidding machine and without moving the skyline to a new anchor point. Frequently, in fact, all logs within several hundred feet of a single anchor point will be skidded without moving either end of the skyline. In prior art devices, such as that disclosed in U.S. Pat. No. 3,948,398, the free end of the drag line is moved to the log to be skidded by having one or more workers pull the free end of the drag line, while the skidding machine is letting out slack.
Although the log skidding capability of prior art log skidding carriages is generally acceptable, it has been found that frequently it is difficult for the workers to pull the heavy drag line the several hundred feet from the carriage to the log to be skidded. The difficulty of the slack pulling task often is exacerbated by extremely rugged terrain and often wet and slippery ground conditions. Specifically, the typical worker comfortably can exert a pull on the drag line of approximately sixty pounds. However, in many operating conditions, a force substantially in excess of sixty pounds is required. For example, in a skidding operation using a 0.46 pound per foot line on a dry ten percent slope, the worker would have to exert a 120 pound force on the line when he is 600 feet from the skidding machine. This required force would be higher for a heavier weight line, a greater distance from the skidding machine, or different slope or ground moisture characteristics.
Workers required to pull excessive forces are susceptible to injuries varying from pulled muscles to more serious injuries resulting from falls. The probability of injury generally increases in proportion to the force the worker is required to exert. As a result, employers either allocate additional personnel for slack pulling tasks, or periodically reallocate personnel from other ongoing responsibilities to assist in slack pulling. The result of either option is increased cost and decreased efficiency.
A few slack pulling devices are available. However, they are very large devices, weighing 1700 to 2500 pounds. Furthermore, they do not meet the mobility and other needs of logging operations.
Accordingly, it is an object of the present invention to improve the efficiency of log skidding operations by providing a new and improved apparatus capable of being manually operated by a worker.
It is another object of the subject invention to minimize the effort required by a worker for slack pulling aspects of log skidding operations.
It is a further object of the subject invention to provide improved safety for workers in the slack pulling aspects of log skidding operations.
It is still another object of the subject invention to provide an apparatus for slack pulling operations that is lightweight, mobile and well adapted to logging operations.